The present invention relates to dosimeter badges for recording radiation dose to sensitive skin layers. It also comprehends the combination of such a dosimeter badge with one that will record dose from more penetrating radiation. Dose from beta radiation is of particular interest as it, except for very high-energy betas, is stopped in the outer surfaces of the individual. However, soft X-rays and gamma may also contribute to skin dose. In determining the radiation dose to an individual, all types of radiation including beta, gamma, X and neutron are of importance and are contemplated for measurement by the various embodiments of the present invention.
Recommended maximum dose for the skin has always been larger than for the whole body. The National Commission for Radiation Protection (NCRP 1971) recommends a maximum of 15 rem to the skin for any one year and a whole body maximum of 5 rem. Recently the International Commission for Radiation Protection (ICRP 1977) has recommended a more complex formula for proportioning doses among various organs but imposes an annual maximum of 50 rem to the skin and 5 rem to the whole body. Thus, when only penetrating or penetrating plus a small amount of low penetrating radiation are involved, precise dosimetry for the less energetic radiation is not particularly important. However, this is not the case for workers exposed to significant levels of beta radiation, for instance as might be produced by exposed mixed fission products or activation products resulting from the development of fission and fusion technology. The measurement of other low penetrating radiation such as soft X-rays is also of continuing importance for technicians using this useful tool in medicine and industry.
Prior efforts to measure low penetrating radiation and skin dose have reflected the lack of emphasis in this area. Beta-sensitive portions of dosimeters are often covered by windows of imprecise, inconsistent or even unknown thickness. Dosimetry estimates are routinely made with window thicknesses in excess of 10 mg/cm.sup.2 to about 100 mg/cm.sup.2 density thickness which are capable of excluding a substantial portion of low-energy betas.
One dosimeter that is currently in use at the Idaho National Engineering Laboratory provides a considerable improvement in distinguishing between penetrating and nonpenetrating radiation. This dosimeter employs a first thermoluminescent dosimeter (TLD) phosphor behind a window of about 4-5 mg/cm.sup.2 density thickness and a second phosphor under about 540 mg/cm.sup.2 of aluminum. Through appropriate calibrations the net readings of the two phosphors correspond somewhat to the nonpenetrating radiation dose. However, one serious shortcoming of this system is that the low penetrating readings are very energy-dependent as a result of relatively high phosphor thicknesses (e.g. 240 mg/cm.sup.2) under each of the windows. This can only be overcome if the dosimeter is calibrated at the same energy levels and in the same type radiation fields to which the wearer is exposed.
The International Commission on Radiation Protection (ICRP) in 1977 selected the range of 5-10 mg/cm.sup.2 as an appropriate skin layer for the determination of absorbed skin dose. Other investigators in this technology have recommended broader and deeper ranges for the consideration of skin dose such that dosimeter designs and methods should accommodate effective dosimetry within this selected range as well as other ranges that subsequently may become of interest.
One suggested dosimeter for measuring radiation dose to the ICRP recommended skin layer employs two thermoluminescent phosphors, one under a 5 mg/cm.sup.2 window and one under a 10 mg/cm.sup.2 window. Unless extremely thin thermoluminescent phosphors become available, the readings made by a dosimeter of this type not only will be energy-dependent but also will be greatly affected by ordinary variations among the different chips. Phosphor chips of about 200-300 mg/cm.sup.2 thickness are ordinarily used. Chips of 100 mg/cm.sup.2 are available but are extremely frangible and result in a very high breakage rate. It is quite apparent that only 5% fluctuation in readings among the various chips may well result in a substantially higher difference in reading than that attributable to the differences in window density thickness. Consequently, this direct approach to dosimetry within a defined but relatively thin layer can be expected to give only a rough indication of dose.